The present invention relates to a hydraulically damping elastomeric bearing suitable for mountings in a motor vehicle.
German Published Patent Application No. 38 21 240 describes an elastomeric bearing, in which an elastic connecting body, for example, made of an elastic or elastomeric plastic or rubber, is arranged between a sleeve-shaped outer first bearing component and an inner second bearing component coaxial to the latter. With the aid of this connecting body, an elastic connection between the first bearing component and the second bearing component is made, which allows relative movements between the bearing components. The conventional elastomeric bearing also includes two chambers which are filled with a liquid damping medium and communicate with one another via a throttle duct. Elastomeric bearings of this type are used in order to mount a vibrating assembly on a non-vibrating holding device. The elastomeric bearings serve, in this context, for vibration insulation or vibration damping. For example, elastomeric bearings of this type are used in vehicle construction, in order to mount vehicle axles, a transmission or an engine on the vehicle body. In this case, one of the bearing components is connected to the vibrating assembly, while the other bearing component is coupled to the non-vibrating holding device. The vibrations of the assembly result in relative movements between the bearing components which reduce the volume of one chamber and at the same time increase the volume of the other chamber. In this case, the liquid damping medium is exchanged correspondingly between the chambers via the throttle duct. The throttling action of the throttle duct results, under these circumstances, in a damping of the relative movement and therefore in a damping of the vibrations capable of being transmitted between the sleeves.
The vibrations to be damped by an elastomeric bearing may have different characteristics, depending on the application. For example, in an elastomeric bearing which is installed in a motor vehicle, vibrations of low frequency and high amplitude, such as, for example, engine shaking vibrations and idling vibrations, may occur, and even high-frequency vibrations of low amplitude which result, for example, in a drumming noise within a passenger compartment of the motor vehicle. The abovementioned German Published Patent Application No. 38 21 240 describes an elastomeric bearing which sufficiently damps both vibrations of low frequency and high amplitude and vibrations of high frequency and low amplitude.
In another application, it may, for example, be necessary to design the elastomeric bearing so that smaller relative movements between the bearing components are damped to a greater extent than larger relative movements. For example, by an elastomeric bearing which is installed in a vehicle, vibrations generated by the vehicle engine are to be damped to a greater extent than vibrations which are caused during the braking or acceleration of the vehicle or by road unevennesses.
It is an object of the present invention to provide an elastomeric bearing that has a different damping behavior for relatively small relative movements between the bearing components from that for relatively large relative movements.
The above and other beneficial objects of the present invention are achieved by providing an elastomeric bearing as described herein. In one example embodiment of the present invention, two chambers of the elastomeric bearing are connected to one another via at least two throttle ducts, one throttle duct containing an absorber which controls the passage or opening cross-section of the other throttle duct. The absorber is mounted in the first throttle duct so as to be adjustable in the longitudinal direction of the throttle duct, the absorber being adjusted as a function of pressure differences at the ends of the first throttle duct and therefore as a function of pressure differences between the chambers connected by the first throttle duct. Pressure differences between the chambers are generated by relative movements between the bearing components. Relative movements between the bearing components correspondingly result in adjustment movements of the absorber. On account of the absorber mass, a specific damping action is thus obtained.
The absorber may, for example, cooperate with the second throttle duct so that, in the case of relatively small relative movements between the bearing components, the absorber blocks the passage cross-section of the second throttle duct, so that the latter does not allow any exchange of damping medium between the chambers. Only when larger relative adjustments occur between the bearing components does the absorber control the passage cross-section of the second throttle duct so that the latter opens to a greater or lesser extent. Correspondingly, in the case of larger relative movements, an exchange of damping medium between the chambers may occur to a greater or lesser extent through the second throttle duct. The result of this is that the elastomeric bearing therefore has a different damping action in the case of larger relative movements between its bearing components from that in the case of smaller relative movements.
In an example embodiment of the present invention, the absorber frees the opening cross-section of the second throttle duct to a greater or lesser extent in the case of smaller relative movements and closes it only in the case of larger relative movements.
The second throttle duct may include a first inlet orifice assigned to the first chamber and a first outlet orifice assigned to the second chamber, the first inlet orifice being connected to the first throttle duct and being controlled by the absorber. By virtue of this arrangement, the control of the inlet orifice or opening cross-section of the inlet orifice may be implemented in a particularly simple manner, since the inlet orifice to be controlled is arranged in the vicinity of the absorber.
The second throttle duct may also include a second inlet orifice assigned to the second chamber and a second outlet orifice assigned to the first chamber, the second inlet orifice being connected to the first throttle duct and being controlled by the absorber. A relatively simple configuration is obtained because of the vicinity of the absorber to the second inlet orifice. In addition, the absorber or the control of the absorber may be configured so that the absorber keeps the first inlet orifice open and the second inlet orifice closed in the case of a sufficient excess pressure in the first chamber and keeps the first inlet orifice closed and the second inlet orifice open in the case of a sufficient excess pressure in the second chamber. In addition, the first outlet orifice may include a first non-return valve which blocks a flow through the second throttle duct from the first outlet orifice to the first inlet orifice and allows a flow from the first inlet orifice to the first outlet orifice. Moreover, the second outlet orifice may include a second non-return valve which blocks a flow through the second throttle duct from the second outlet orifice to the second inlet orifice and allows a flow from the second inlet orifice to the second outlet orifice. The selected alternate control of the two inlet orifices by the absorber and the selected arrangement of the non-return valves ensure that the flow may pass through the second throttle duct in both directions, the control of the throughflow cross-section being implemented by the absorber simultaneously for both directions of throughflow. A form of construction of this type may be made highly compact.
Alternatively, in an example embodiment of the present invention, the first throttle duct includes the absorber, the second throttle duct includes a first inlet orifice assigned to the first chamber and a first outlet orifice assigned to the second chamber, the first inlet orifice being connected to the first throttle duct and being controlled by the absorber, and a third throttle duct is provided, which connects the two chambers in parallel to the first throttle duct and to the second throttle duct and which has a second inlet orifice assigned to the second chamber and a second outlet orifice assigned to the first chamber, the second inlet orifice being connected to the first throttle duct and being controlled by the absorber. The absorber is configured so that it keeps the first inlet orifice open and the second inlet orifice closed in the case of a sufficient excess pressure in the first chamber and keeps the first inlet orifice closed and the second inlet orifice open in the case of a sufficient excess pressure in the second chamber. This example embodiment of the present invention, in contrast to that described above, manages without non-return valves, so that a simpler construction is obtained for the elastomeric bearing. This example embodiment of the present invention may include non-return valves which are accommodated in the second throttle duct or in the third throttle duct.
In the elastomeric bearing according to the present invention, at least one of the non-return valves may configured as an excess-pressure valve and allow a flow through the respective throttle duct from the respective inlet orifice to the associated outlet orifice only beyond a predetermined excess pressure on the inlet side. The damping characteristic of the elastomeric bearing may be additionally influenced as a result of this arrangement.
The first inlet orifice may issue into the first throttle duct within the range of adjustment of a first end portion, assigned to the first chamber, of the absorber, the throughflow opening cross-section of the first inlet orifice being controlled by a greater or lesser overlap by the first absorber end portion. The absorber thereby directly controls the first inlet orifice and therefore the opening cross-section of the second throttle duct. A throttle duct arrangement of this type may have a particularly compact construction.
The second inlet orifice may issue into the first throttle duct within the range of adjustment of a second end portion, assigned to the second chamber of the absorber, the throughflow opening cross-section of the second inlet orifice being controlled by a greater or lesser overlap by the second absorber end portion. Particularly in combination with the features of the abovementioned example embodiment of the present invention, this arrangement results in a particularly compact form of construction for the throttle duct arrangement.
According to another example embodiment of the present invention, the absorber may be prestressed into an initial position by a spring device. A predetermined initial position is defined with the aid of this arrangement, as a result of which the damping behavior of the elastomeric bearing may be reproduced.
The initial position of the absorber may be selected such that, in this initial position, the absorber closes both inlet orifices. Correspondingly, in both possible directions of movement of the relative movements between the two bearing components, first only the damping action of the first throttle duct, with the absorber adjustable in it, is activated, while, in the event of larger relative adjustments, i.e., in the event of greater pressure differences, the throttling action of the second throttle duct or the third throttle duct, if present, is activated.
Where a particularly compact form of construction is concerned, the first outlet orifice may be connected to the first throttle duct, the first outlet orifice then issuing into the first throttle duct outside the range of adjustment of a second end portion, assigned to the second chamber, of the absorber. In addition, the second outlet orifice may also be connected to the first throttle duct, in which case the second outlet orifice also issues into the first throttle duct outside the range of adjustment of a first end portion, assigned to the first chamber, of the absorber. This arrangement results in a compact form of construction for the throttle duct arrangement.
The features mentioned above and those explained below may be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.